1. Technical Field
The present invention relates to a resist composition used in a photolithography process, and more particularly, to a resist composition for use as a bottom-layer resist used in a bi-layer resist process.
2. Discussion of the Related Art
As semiconductor devices become more highly integrated, the ability to form very fine patterns in a photolithography process becomes more important. For example, to fabricate semiconductor devices of a scale of one gigabit or greater, a pattern size having a design rule of 0.2 μm or less is needed. Further, light sources having a short wavelength, such as an ArF excimer laser (λ=193 nm) or a F2 (λ=157 nm) laser, have been proposed instead of a KrF excimer laser (λ=248 nm), which is a conventional light source of deep ultra violet (DUV) light.
Further, resist compositions for ArF or F2 light sources have suffered from a variety of drawbacks when used in a photolithography process in comparison with conventional resist compositions for the KrF or i-line (λ=365 nm) light sources. For example, the resist compositions have a weak resistance to a dry etching process and an increase in pattern collapse as an aspect ratio of pattern features increases. Thus, there is a need for new resist compositions and processes for using the same to prevent the above-identified problems.
Generally, in a photolithography process for the manufacture of highly integrated semiconductor devices, there are two types of processes widely used. One is a single-layer resist (SLR) process and another is a bi-layer resist (BLR) process. In a SLR process, a photoresist pattern is formed by patterning a photoresist layer using one photolithography process and a desired layer is directly patterned by using the patterned photoresist. In a BLR process, a bottom-layer resist and a top-layer photoresist are sequentially stacked. The top-layer photoresist is patterned by a photolithography process to form a top-layer photoresist pattern. The bottom-layer resist is patterned by using the top-layer photoresist pattern as a mask during an etching process, thereby forming a bottom-layer resist pattern. And then, a desired layer is patterned by using the bottom-layer resist pattern as a mask during an etching process. The top-layer photoresist in the BLR process is thinner than a photoresist layer in a SLR process. Thus, the top-layer photoresist pattern is not collapsed and is able to form finer patterns. The bottom-layer resist functions as an anti-refractive layer during the photolithography process with respect to the top-layer photoresist and functions as an etch mask while patterning a subsequent desired layer.
Further, in a BLR process using a light source having a wavelength of 248 nm, a novolak resin is usually employed as a bottom-layer resist. At a wavelength of 248 nm, the novolak resin has been well known to have superior anti-refractivity and dry-etch resistance while patterning a layer formed of an inorganic material. However, the novolak resin has a high refractivity of greater than 10% at a wavelength of 193 nm or below, thereby being incongruent as a bottom-layer resist when used in conjunction with a wavelength of 193 nm or below.
Therefore, a need exists for a resist composition to be used as a bottom-layer resist in a bi-layer resist process that provides an increase in resistance to a dry-etching process and a decrease in pattern collapse as an aspect ratio increases as pattern features of a device also increase. Further, there is also a need for a resist composition to be used as a bottom-layer resist in a BLR process using a photolithography process employing a light source having a wavelength region of 193 nm or below while improving a dry-etch resistance and decreasing pattern collapse of a resist composition.